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Chapter 14: Q19P (page 729)

Show how you would use a protecting group to convert 4-bromobutan-1-ol to hept-5-yn-1-ol.

Short Answer

Expert verified

Triisopropylsilyl chloride is used as protecting group for the protection of hydroxyl group. Base is used to abstract the proton from hydroxyl and convert it into good nucleophile so that attack of nucleophile can be easily facilitated on TIPS group.


Protection of hydroxyl group using TIPS chloride as protecting group

Step by step solution

01

Step-1. Protection of hydroxyl group in 4-bromobutan-1-ol:

Triisopropylsilyl chloride is used as protecting group for the protection of hydroxyl group. Base is used to abstract the proton from hydroxyl and convert it into good nucleophile so that attack of nucleophile can be easily facilitated on TIPS group.


Protection of hydroxyl group using TIPS chloride as protecting group

02

Step-2. SN2 attack and deprotection of protecting group:

Propyne on treatment with sodium amide which acts as a base abstracts acidic proton from terminal alkyne and converts it into good nucleophile which attacks at the product formed in first step, and forms another product which further on deprotection with tetra-n-butylammonium fluoride forms the required product, that is, hept-5-yn-1-ol.

Formation of the product hept-5-yn-1-ol

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Most popular questions from this chapter

Question. Propose a complete mechanism for the reaction of cyclopentene oxide with sodium methoxide in methanol.

(a) Tetramethyloxirane is too hindered to undergo nucleophilic substitution by the hindered alkoxide, potassium tert-butoxide. Instead, the product is the allylic alcohol shown. Propose a mechanism to explain this reaction. What type of mechanism does it follow?

(b) Under mild acid catalysis, 1,1-diphenyloxirane undergoes a smooth conversion to diphenylethanal (diphenylacetaldehyde). Propose a mechanism for this reaction. (Hint: Think Pinacol.)

Propylene oxide is a chiral molecule. Hydrolysis of propylene oxide gives propylene glycol, another chiral molecule.

(a) Draw the enantiomers of propylene oxide.

(b) Propose a mechanism for the acid-catalyzed hydrolysis of pure (R)-propyleneoxide.

(c) Propose a mechanism for the base-catalyzed hydrolysis of pure (R)-propyleneoxide.

(d) Explain why the acid-catalyzed hydrolysis of optically active propylene oxide gives a product with lower enantiomeric excess and a rotation opposite that of the product of the base- catalyzed hydrolysis.

Boron tribromide(BBr3)cleaves ethers to give alkyl halides and alcohols.

The reaction is thought to involve attack by a bromide ion on the Lewis acid-base adduct of the ether with(BBr3)(a strong Lewis acid). Propose a mechanism for the reaction of butyl methyl ether with(BBr3)to give (after hydrolysis) butan-1-ol and bromomethane.

Predict the major product when each reagent reacts with ethylene oxide.

(a) NaOCH2CH3(Sodium ethoxide)

(b) NaNH2(sodium amide)

(c) NaSPh (sodium thiophenoxide)

(d) PhNH2(aniline)

(e) KCN (potassium cyanide)

(f) NaN3(soidum azide)
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